This invention relates to bonded structures including a self-aligned liner that bonds metal pads located on each side of bonded substrates and methods of manufacturing the same.
Bonding of multiple substrates is required to enable three-dimensional integration of chips. Bonding of two substrates can be effected by adhesion between two dielectric materials as in an oxide-to-oxide bonding that fuses silicon dioxide materials from two substrates after bonding, by adhesion between two metallic materials as in a copper-to-copper bonding that employs direct contact between two copper pads and a subsequent grain growth across the original interface between the two copper pads, or by a method employing a combination of the two adhesion mechanisms.
The effectiveness of currently available bonding methods is limited by the bonding strength, i.e., the mechanical adhesion strength, between the two substrates that are bonded together. Because substrates including semiconductor devices are bonded after semiconductor devices are fully formed within each substrate, the temperature of bonded substrates cannot be raised above a certain limit, typically about 250° C., without adversely affecting semiconductor devices or dielectric material in the substrates. The constraint on the processing temperature after bonding of substrates limits the effectiveness of the fusing of dielectric materials or grain growth of metal across the original bonding interface. However, high mechanical adhesion strength across two bonded substrates is needed to insure reliability in the physical integrity of bonded substrate.